This invention relates to a method for producing a hose and, more particularly, a hose embodying a metallic reinforcement layer. The hose of the invention has a wide variety of applications but one widespread use is for the delivery of hydraulic fluid--as for example hydraulic systems for farm and construction equipment.
In recent years, the practice in the thermoplastic hose industry has been to use fibrous materials as the reinforcing layer such as polyethylene terephthalate polyester fibers known as "Dacron". More recently, aromatic polyamides such as "Kevlar" have been employed as the reinforcing layers in thermoplastic hoses. The reinforcement layer imparts strength and burst resistance to the hose. It is desirable to provide a reinforcement layer which provides substantial kink resistance in the hose and which is still satisfactorily flexible while yet providing the desirable reinforcement function.
A large number of different types of hose constructions have been developed over the years providing different desirable features and utilizing a wide range of materials. Further, a number of different techniques have been utilized for bonding the reinforcement layer to the outer surface of the core tube. A recent example of a reinforcement layer which is mechanically interlocked with the core tube is U.S. Pat. No. 3,944,453 of Chudgar et al. However, the teaching there required the use of a specially thermally formed, fused bonding layer.
Another example of a mechanically interlocked type of reinforced thermoplastic hose but which again requires a special layer is U.S. Pat. No. 3,945,867 of Heller et al.
Provided concurrently with the fibrous reinforcement type of thermoplastic hose have been rubber hoses equipped with metallic or wire reinforcements. Illustrative of the teachings of wire reinforced rubber hose is U.S. Pat. No. 3,776,794 of Ingham. There, the core tube must be first supported by an internal mandrel and thereafter must be cured.
In some instances metallic reinforcements have been provided on core tubes constructed of materials other than rubber (such as thermoplastics) but the bond has either been nonexistent or very poor. It is to this last form of hose to which the invention is directed, i.e., the production of a hose wherein a metallic reinforcement is mechanically interlocked with a thermoplastic core tube and advantageously also, to the cover.
According to the invention, the thermoplastic core tube has an outer surface to which is applied an intersticed metallic reinforcement, after which the core tube is heated in selected portions adjacent its outer surface (as by induction heating) so as to soften the portions adjacent the outer surface for migration into the interstices. Thereafter, the migrant portions are cooled to form a uniform (i.e., solvent-free) mechanical interlock between the core tube and the reinforcement. The advantage of such an improved interlock which serves to maintain the integrity of the composite structure is to provide kink-resistance and better performance under pressure impulse conditions. When covered with material compatible with the core tube material, heat from the extruded cover softens the migrant portions to provide a fusion bond between the cover and the migrant portions.
Other objects and advantages of the invention may be seen in the details of construction and operation as set down in the ensuing portion of the specification.